Probing Parton Dynamics of QCD Matter with $\Omega$ and $\phi$ Production

TL;DR

This study investigates strange hadron production in heavy-ion collisions at various energies to understand the transition from quark-gluon plasma to hadronic matter, revealing energy-dependent changes in strange quark dynamics.

Contribution

It provides new measurements of $ ext{Ω}$ and $ ext{ϕ}$ production across multiple energies, highlighting deviations in strange quark behavior below 19.6 GeV.

Findings

Deviations in particle ratios at lower energies and peripheral collisions.

Suppression of strange quark production at 11.5 GeV in central collisions.

Significant changes in strange quark distributions below 19.6 GeV.

Abstract

We present measurements of $\Omega$ and $\phi$ production at mid-rapidity from Au+Au collisions at nucleon-nucleon center-of-mass energies $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27 and 39 GeV by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). Motivated by the coalescence formation mechanism for these strange hadrons, we study the ratios of $N(\Omega^{-}+\Omega^{+})/(2N(\phi))$. These ratios as a function of transverse momentum ($p_T$) fall on a consistent trend at high collision energies, but start to show deviations in peripheral collisions at $\sqrt{s_{NN}}$ = 19.6, 27 and 39 GeV, and in central collisions at 11.5 GeV in the intermediate $p_T$ region of 2.4-3.6 GeV/c. We further evaluate empirically the strange quark $p_T$ distributions at hadronization by studying the $\Omega/\phi$ ratios scaled by the number of constituent quarks. The NCQ-scaled $\Omega/\phi$ ratios show a suppression of strange quark production in central collisions at 11.5 GeV compared to $\sqrt{s_{NN}} >= 19.6$ GeV. The shapes of the presumably thermal strange quark distributions in 0-60% most central collisions at 7.7 GeV show significant deviations from those in 0-10% most central collisions at higher energies. These features suggest that there is likely a change of the underlying strange quark dynamics in the transition from quark-matter to hadronic matter at collision energies below 19.6 GeV.